The simple answer is no, it wouldn't work.
Vegetable shortening is 100% fat. Peanut butter contains significant amounts of protein and starch, and carries a profound peanut flavor. These are going to drastically change any recipe it is used in lieu of shortening.
If you desire lower fat recipes, I suggest you look specifically for recipes designed with that aspect in mind.
Melting point is typically only significant in baking in two circumstances:
- Use of the creaming method where sugar is cut into fat incorporating air as part of the leavening process
- Making of laminated doughs such as puff pastry, croissants, or strudels
Peanut butter is a complex food, but the oil phase is either already liquid (in room temperature so-called "natural" peanut butters, or only contains a small amount of saturated fats in typical commercial peanut butters, and so has a lower melting point that pure hydrogenated vegetable shortening.)
Neither of these typically apply to cookies.
Consistency is harder to predict. It depends on what is being cooked, but peanut butter has less fat than shortening (since shortening is pure fat, and peanut butter has a high percentage of peanut solids, starches and proteins for the most part).
The interaction of these various components in the chemistry of the actual product will determine the consistency.